This invention is related to a composite material comprising one or more discontinuous phases of wood particles encapsulated in a polymeric matrix, and also methods and equipment for manufacturing same. In one aspect, it relates to a composite material comprising two discontinuous wood phases having distinct size ranges encapsulated in a thermoplastic polymeric matrix.
Composite materials consisting of natural wood fibers or particles held together with a binder substance have been widely used in the construction industry for many years and are produced on a world-wide basis. Specific examples of these composite materials, which may also be referred to as xe2x80x9ccomposite woodxe2x80x9d, include: plywood, which is made from thin sheets of virgin wood fibers pressed together with a thermoset resin binder; particle board, made using finely ground virgin wood particles pressed together with a thermoset resin binder; oriented strand board, made from thin oriented virgin wood wafers pressed together with a thermoset resin binder; and medium and high density fiberboard, made from virgin wood particles pressed together with a thermoset resin binder.
More recently, a composite wood material has been produced using finely ground wood particles, also known as wood xe2x80x9cflourxe2x80x9d, encapsulated in a thermoplastic matrix. The composite wood is essentially a thermoplastic material mixed, or xe2x80x9ccompoundedxe2x80x9d, together with a wood flour filler material. The compounding of thermoplastics with filler material has been carried out for many years to modify the physical properties of thermoplastics. The compounding of thermoplastics with finely ground wood flour particles can produce a composite wood material having certain physical properties which are superior to natural wood, for example, reduced water absorption, improved resistance to chemical degradation, improved resistance to rot, and improved resistance to termites and other wood damaging insects. Due to these superior physical properties, compounded thermoplastic composite wood materials are currently used in many applications, for example, exterior door and window frames, furniture, decking, boardwalks, siding and trim materials.
While exhibiting certain desirable physical properties, compounded thermoplastic composite wood materials currently being produced typically have a density that is significantly greater than natural wood. For example, some existing thermoplastic composite wood materials have a density that is 60% greater than natural wood. Further, these materials are generally not recommended for use in load-bearing or structural applications because the thermoplastic is the primary structural component and it deforms excessively under loaded conditions. Typically, the amount of wood flour filler in the thermoplastic matrix is generally in the range of 50% by weight and the encapsulated wood particles are about 40-60 mesh (i.e., about 0.016-0.010 inch) in size. In order to reduce the overall weight of products made using these dense thermoplastic wood composite materials, the finished product design often includes thin walls with hollow spaces and structural support webs. In some cases, a foaming agent is added to the thermoplastic to reduce the density of the material. However, such foaming agents and thin-wall designs can result in a significant reduction in the impact and/or shear strength properties of the products made using these thermoplastic composite wood materials.
Notwithstanding the composite materials previously disclosed by others, their remains a need for thermoplastic composite wood materials having improved density, impact resistance, flex-modulus, compression strength, and/or shear strength properties in comparison to current materials.
A need further exists, for methods of producing thermoplastic composite wood materials having the improved characteristics described above.
A need still further exists for equipment useful in the production of thermoplastic composite wood materials, or alternately in processes where the controlled dispensing of high viscosity materials is required.
The present invention disclosed and claimed herein, in one aspect thereof comprises a composite material including a first wood component, a second wood component and a thermoplastic polymer component. The first wood component is of substantially axially aligned wood chips having a first size range and being distributed throughout the composite material in a first discontinuous phase. The second wood component is of wood particles having a second size range and being distributed between the wood chips in a second discontinuous phase, the second size range being distinct from the first size range and having substantially smaller values than the first size range. The thermoplastic polymer component encapsulates the wood chips and the wood particles and forms a continuous phase extending throughout the composite material. The wood chips constitute from about 100 to about 0 weight percent of a total weight of the first and second wood components and the wood particles constitute from about 0 to about 100 weight percent of the total weight of the first and second wood components. The first and second wood components together constitute from about 90 to about 50 weight percent of the composite material. The thermoplastic polymer component constitutes from about 10 to about 50 weight percent of the composite material.
In another aspect, the invention comprises a composite material including an inner structural member and an outer structural member. The inner structural member has a first wood component of substantially axially aligned wood chips having a first size range and being distributed throughout the inner structural member in a first discontinuous phase. A second wood component of wood particles having a second size range is distributed between the wood chips in a second discontinuous phase, the second size range being distinct from the first size range and having substantially smaller values than the first size range. A first thermoplastic polymer component encapsulates the wood chips of the first wood component and the wood particles of the second wood component and forms a first continuous phase extending throughout the first structural member. The first and second wood components together constitute from about 90 to about 50 weight percent of the inner structural member, and the first thermoplastic polymer component constitutes from about 10 to about 50 weight percent of the inner structural member. The outer structural member is continuously joined to the inner structural member. The outer structural member includes a third wood component of wood particles having a third size range and being distributed throughout the outer structural member in a third discontinuous phase. A second thermoplastic polymer component encapsulates the wood particles of the third wood component and forms a second continuous phase extending throughout the outer structural member. The third wood component constitutes from about 10 to about 50 weight percent of the outer structural member, and the second thermoplastic polymer component constitutes from about 90 to about 50 weight percent of the outer structural member.
In yet another aspect, the invention comprises a method of manufacturing a thermoplastic composite wood material comprising an inner structural member including substantially axially aligned wood chips having a first size range, a second wood component of wood particles having a second size range, and a first thermoplastic polymer component encapsulating the wood chips and the wood particles and forming a first continuous phase extending throughout the first structural member. The method includes the step of mixing together a first quantity of a first wood component of wood chips having long axes and a first size range, a second quantity of a second wood component of wood particles having a second size range distinct from the first size range, and a third quantity of a first thermoplastic polymer component of molten thermoplastic polymer until substantially all of the wood chips and the wood particles are encapsulated by the thermoplastic polymer. It further includes the step of orienting the long axes of the wood chips of the first wood component such that they are substantially parallel to a predetermined plane. It further includes the step of depositing a loose material constituting a mixture of the wood chips encapsulated in the thermoplastic polymer and the wood particles encapsulated in the thermoplastic polymer onto a press inlet conveyor unit while maintaining the orientation of the long axes of the wood chips. It further includes the step of pressing the loose material in a direction substantially parallel to the predetermined plane such that it is compacted and such that the long axes of the wood chips are oriented substantially parallel to one another.
In still another aspect, the invention comprises a method of manufacturing a thermoplastic composite wood material comprising an inner structural member and an outer structural member, where the inner structural member includes a first wood component of substantially axially aligned wood chips having a first size range and being distributed throughout the inner structural member in a first discontinuous phase, where the inner structural member also includes a second wood component of wood particles having a second size range and being distributed between the wood chips in a second discontinuous phase, and where the inner structural member also includes a first thermoplastic component encapsulating the wood chips and the wood particles and forming a first continuous phase extending throughout the inner structural member, and further where the outer structural member is continuously joined to the inner structural member and includes a third wood component of wood particles having a third size range and a second thermoplastic component encapsulating the wood particles of the third wood component and forming a second continuous phase extending throughout the outer structural member. The method comprises the step of mixing together a first quantity of a first wood component of wood chips having long axes and a first size range, a second quantity of a second wood component of wood particles having a second size range distinct from the first size range, and a third quantity of a first thermoplastic component of molten thermoplastic, until substantially all of the wood chips and the wood particles are encapsulated by the thermoplastic. It further includes the step of orienting the long axes of the wood chips of the first wood component such that they are substantially parallel to a predetermined plane. It further includes the step of depositing a loose material constituting a mixture of the wood chips encapsulated in the thermoplastic and the wood particles encapsulated in the thermoplastic onto a press inlet feed unit while maintaining the orientation of the long axes of the wood chips. It further includes the step of pressing the loose material in a direction substantially parallel to the predetermined plane such that it is compacted and such that the long axes of the wood chips are aligned substantially parallel to one another, thereby forming an inner structural member. It further includes the step of mixing together a fourth quantity of a third wood component of wood particles having a third size range and a fifth quantity of a second thermoplastic component of molten thermoplastic until substantially all of the wood particles are encapsulated by the thermoplastic. It further includes the step of joining the material formed by mixing the third wood component and the second thermoplastic to the inner structural member.
In still another aspect, the invention comprises a compounder unit for mixing and orienting shaped pieces within a viscous material. The compounder unit comprises an outer casing having exterior walls defining a longitudinal cavity therein, the cavity being subdivided into a material inlet section, a mixing section, an orientation section, and an outlet passage and having a long axis passing therethrough. At least one compounding shaft is positioned within the longitudinal cavity parallel to the long axis, the compounding shaft having a plurality of blades formed thereon. The blades on a portion of compounding shaft within the orientation section include screw blades having a pitch which progressively decreases as the distance from the blade position to the outlet passage decreases.
In still another aspect, the invention comprises a coating die apparatus for extruding a viscous materials. The apparatus comprises an exterior casing that defines a longitudinal cavity and a shaft rotatably mounted in the cavity. The shaft has a plurality of mixing elements mounted thereon defining a feed section and a dispensing section. The mixing elements in the feed section have a positive pitch for urging molten material received into the feed section of the cavity into the dispensing section of the cavity and the mixing elements in the dispensing section urge molten material received in the dispensing section tangentially against the interior of the exterior casing. The exterior casing further defines a dispensing slot formed tangentially through the exterior casing and extending longitudinally across the dispensing section. Molten material received into the dispensing section is sliced off by the exposed inner edge of the casing to form a raw sheet of molten material which exits the dispensing slot.